Selective oxidation of diclofenac sodium with different electronegative moieties via coexisting SO4− and OH

The selective oxidation capacity of free radicals in advanced oxidation processes (AOPs) is important for the accurate determination of the degradation pathways of organic contaminants when various active species coexist in the catalytic system. In this study, diclofenac sodium (DCF) was selected as a model contaminant due to its toxicity and structural characteristics (containing organic moieties with varying electronegativity). A 3D hexagonal star-shaped cobalt oxide electrode was synthesized and used as the electric anode to simultaneously combine with AOPs based on peroxymonosulfate (EAOPs/PMS) to generate two active species (SO4− and OH) and achieve efficient mineralization of DCF. The selectivity property of the free radicals was investigated by comparing DCF transformation pathways in three systems: EAOPs/PMS (containing both SO4− and OH), EAOPs/PMS + TBA (containing only SO4−), and Fe2+/H2O2 (containing only OH). When present simultaneously, SO4− favored attacking the electron-donating moieties (amino groups and aromatic rings), while OH was more disposed to attack the electron-withdrawing moieties (carboxyl groups and chlorine atoms). This study, for the first time, sheds light on the selective oxidation capacity of coexisting SO4− and OH towards organic moieties with differing electronegativity and provides an in-depth analysis of the degradation pathways of an organic contaminant. [Display omitted] •The selective oxidation of co-existing SO4− and OH was systematically explored for the first time.•The efficient mineralization of DCF could be achieved in the EAOPs/PMS system.•Through comparing the DCF transformation pathways in three systems, the selective oxidation of SO4− and OH was well investigated.•When they were present simultaneously, SO4− favored to attack on the electron-donating moieties, while OH was disposed to attack the electron-drawing moieties.